With the evolution of the 3rd Generation (3G) air interface technologies, the transmission speed of the air interface is greatly increased and the throughput of Packet Switched (PS, Packet Switched) traffic is multiplied. Core Net (CN, Core Net) nodes such as the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN), value-added servers (VASs), and the transport bearers between the nodes are faced with unprecedented loads. Taking the Internet with rich contents for example, Internet traffic imposes higher requirements on the transmission bandwidth of the CN, so that the cost of capacity expansion rises rapidly. The Internet traffic occupies many transport resources of the mobile network but creates low profit for the mobile operator. Furthermore, when a user accesses an Internet service via a Packet Data Network (PDN, Packet Data Network), data packets need to pass through many CN nodes, so that the efficiency of transmission is low.
To relieve the bearing burden of CN nodes and increase the packet transmission efficiency of PS services, the existing technical solution adds a logical function between a Radio Network Controller (RNC) and an SGSN to offload data traffic flows of a user. This logical function is a Traffic Offload Function (TOF) which routes uplink Internet traffic directly to a PDN in a low-cost manner at a node close to the access network, and routes downlink traffic from the PDN directly to the access network, so as to offload the data traffic on the CN. FIG. 1 illustrates a network architecture of this solution. In FIG. 1, the TOF is a logical function. In embodiments of the present invention, the entity in which a TOF is deployed is described as a TOF entity. The TOF entity may be deployed on the Iu-PS interface between an RNC or a Home NodeB Gateway (HNB GW) and an SGSN in a Universal Mobile Telecommunications System (UMTS). The TOF entity provides a standard Iu interface to both the RNC/HNB GW (RNC or HNB GW) and the SGSN and provides a Gi interface to fulfill the traffic offload function. The Charging Gateway (CG) and Lawful Interception Gateway (LIG) provide open interfaces to the TOF. To further reduce the transport bearers between the RNC/HNB GW and the TOF, the TOF can be integrated with the RNC/HNB GW.
In the prior art, for a network that uses a traffic offload function, if the state of a User Equipment (UE) changes, for example, changes from an active state to an idle state, or if the parameters stored by the TOF entity are updated, the communication between the CN and the UE will be interrupted. For example, if the UE is attached to the network via TOF entity 1, when the UE moves from TOF entity 1 to TOF entity 2 (TOF2) in the idle state, the UE initiates a traffic offload service request and enables the traffic offload. Afterwards, the UE that changes to the idle state receives downlink packets of the offload traffic under TOF 2. At this time, TOF 2 must page the UE and restore the data transmission of the UE to support traffic continuity. That is, if traffic is offloaded at TOF 2, the UE is using the traffic offload before the UE changes to the idle state. When no data transmission exists for a period of time, the air interface resource will be released and enters into the idle state. However, the application connection is not released, and the TOF will probably still receive the downlink packets of the offload traffic. To guarantee the service can be used continuously, the TOF needs to instruct the UE to set up a bearer with the network. Or, the UE does not move to TOF 2 and remains at TOF 1 but the state of the UE has changed. For example, after the traffic offload of the TOF is completed, the UE enters into the idle state. At this time, the air interface resource between the UE and the CN is also released. However, because the application connection is not released, when the UE receives new packets of the offload traffic again, the UE needs to restore the connection with the CN to implement the transmission of packets of the offload traffic.
From the above description, the TOF traffic offload causes communication interruption between the CN and the UE because of the release of the air interface resource.